Secured institutions such as minimum security prisons or high security commercial installations have many cells or rooms which must be individually locked and unlocked for controlled access of inmates, patients or employees. It is generally desirable in such systems to provide a central control center, for example a guard station, which monitors the conditions of each individual lock and which remotely and selectively locks and unlocks the doors, for example by means of solenoids.
In present security locking systems, a solenoid is coupled to a lock mechanism and is energized and de-energized to control the movement of the latchbolt or deadbolt of the lock. If the locking mechanism is constructed or "fail-safe" operation, the latchbolt or deadbolt is mechanically biased to unlock the door when the solenoid is de-energized. Thus, the door will remain locked only for so long as the solenoid is energized.
If the locking mechanism is constructed for operation in a "fail-secure" mode, the latchbolt or deadbolt is mechanically biased to lock the door when the solenoid is de-energized. Thus, if power fails, the door remains locked.
Solenoid-actuated locks have heretofore required different mechanical and electrical designs to provide fail-secure or fail-safe modes of operation. Thus, lock manufacturers have had to maintain separate parts inventories and have had to use different assembly operations for fail-safe and fail-secure types of locks. These relatively expensive manufacturing and inventory requirements have added to the cost of the locks. In addition, if a security institution at some point desires to change the mode of operation of its locks, a substantial amount of time has been required to replace or modify locking mechanisms to achieve the desired change in function.
Accordingly, it is an object of the invention to provide a solenoid-actuated security lock which can be easily modified to operate in either the fail-safe or fail-secure mode.
It is another object of the invention to provide such a lock which is relatively simple to construct and which is reliable in operation.
A further object of the invention is to provide a security lock which has essentially the same components and assembly operations for either its fail-safe or fail-secure versions.
In institutional locks it is desirable and in many cases mandatory to provide a deadlock lever mechanism for mechanically blocking retraction of an extended deadbolt or latchbolt. The blocking action of the deadlock lever prevents an inmate from unlocking the door by forcing the latchbolt or deadbolt back into its casing. The deadlock lever thus provides a positive locking operation and resists tampering which might otherwise result in unlocking a secured door.
Industry design standards also require a relatively small thickness or profile for the housing of a lock. In order to provide a lock with a low profile housing and deadlocking capability, it has been necessary in many cases to use deadbolts and latchbolts with a relatively small extension or "throw" of, for example, less than three-quarters of an inch (1.905 cm). A bolt throw of at least three-quarters of an inch should be required for most medium security applications and in some cases the throw should be extended to one inch (2.54 cm).
Accordingly, it is an object of the invention to provide a relatively low profile lock which uses a bolt with either a three-quarter or a one inch extension.
From a manufacturing standpoint, it is desirable to provide a lock which can operate with either a three-quarter inch latchbolt or a one inch deadbolt, in order to accommodate the differing requirements of security institutions. However, it has been difficult to provide a single mechanism which will operate reliably with bolts having different throw lengths, because a change in throw length can alter the timing of movement of components within the lock.
Accordingly, it is a further object of the invention to provide a locking mechanism which can be easily modified to reliably utilize either a one inch deadbolt or a three-quarter inch latchbolt.
If a latchbolt is used in association with a deadlock lever, it is desirable to provide a symmetrical engagement of the lever and the bolt to ensure a positive blocking action. If the deadlock lever is of a pivoting type, it is particularly important to provide contact with the latchbolt on opposite sides of the lever's pivot point.
Accordingly, it is another object of the invention to provide a locking mechanism with a pivoting deadlock lever which contacts a latchbolt at points on opposite sides of the pivot point of the lever.
It has been found convenient in prior art locks to employ a bolt which supports its deadlock lever when the bolt is retracted into the housing of the lock. Thus, when the bolt is retracted, it will slide over the deadlock lever until it reaches it fully retracted position. This sliding engagement is undesirable, because it frictionally resists retraction of the bolt and could conceivably result in binding between the latchbolt and deadlock lever.
Accordingly, it is an object of the invention to provide an improved security lock wherein the deadlock lever is spaced from its associated latchbolt or deadbolt. The spaced relation of the components ensures that the bolt can be easily and fully extended to provide a positive deadlock and can be easily retracted into the lock housing to unlock a door.
Binding between a latchbolt or deadbolt and the deadlock lever can also occur if the lever fails to move away from the bolt when the bolt is being retracted within the lock housing to unlock a door. It is therefore an object of the invention to provide a lock with a relatively simple and reliable mechanism which allows full disengagement of the lever from the bolt before the bolt is retracted into the housing of the lock.
A security lock may malfunction if its switch components shift slightly in position as a result of vibration. Malfunctions of this type are typically corrected by the costly and time consuming process of disassembling the lock and replacing or realigning the components.
It is therefore an object of the invention to provide a lock with switch components which can be easily adjusted to position without opening the housing of the lock.
Malfunctions can also occur as a result of wear of lock components in use. Malfunctions of this type have typically required replacement of the component or of the entire lock.
It is therefore an object of the invention to provide a lock with components which can be adjusted to compensate for wear.
In field installation of locks, the gap between doors and associated doorjambs may vary considerably from door to door. If a lock has a triggerbolt with a fixed extension, the variation in door gap can provide serious installation problems. Moreover, in field installation, doors may have strikeplates oriented in reversed positions. If a lock has a triggerbolt which is supported in a fixed orientation, it can be used only with doors having strikeplates aligned to accept this particular positioning of the triggerbolt.
Accordingly, it is an object of the invention to provide a security lock with a triggerbolt which has an adjustable extension to accommodate different door gaps and which can be reversed in orientation to operate with strikeplates of different orientation.
The solenoid which operates a security lock typically has a high current coil to provide a momentary powerful thrust for moving a latchbolt or deadbolt against a biasing spring. After the bolt has changed its position, a second coil is connected to provide a low holding current which maintains the bolt in position. If the mechanism which switches the coils malfunctions, the solenoid may be continuously operated at a high current. The heat generated by the constant high current can damage the solenoid or create a serious fire hazard.
Accordingly, it is an object of the invention to provide a solenoid-actuated lock with a thermal protector which reduces the operational current of the solenoid when a dangerous heating condition is sensed. The thermal protector thus prevents undesirable heating while continuing to power the lock.